1. Field of the Invention
The present invention relates to an improvement in the structure of a temperature sensitive fluid-type fan coupling device wherein external temperature is constantly sensed while a vehicle is travelling so as to provide a controlled amount of cooling air to an antomobile engine by a cooling fan.
2. Description of the Prior Art
FIGS. 7 and 8 show the principal part of a conventional fan coupling device of this type. As illustrated, an oil chamber 26 is defined above a partition 25. The partition 25 has an opening 25' through which the oil chamber 26 is in communication with a torque transmission chamber 24. A temperature sensitive element is mounted to the front of a closed enclosure and is deformed in response to temperature fluctuation. A valve element 28 has a fixed end and is moved by the temperature sensitive element to open the opening 25' when external temperature exceeds a given temperature.
With such a conventional device, a connecting element (not shown) is connected to the valve element 28 so that the valve element 28 is movable when the temperature sensitive element is deformed. Also, the valve element is so wide as to open and close the opening 25'. Due to mutual engagement in a plane extending at right angles to the direction in which the flat and wide valve element 28 is displaced relative to the opening 25', a centrifugal force is applied to pressurize oil which flows from the oil chamber 26 to the torque transmission chamber 24 during opening and closing of the valve element 28. The resultant back pressure causes suction of the valve element 28 to close the opening 25'. This results in a decrease in the amount of oil in the torque transmission chamber 34. Torque is then less transmitted to reduce the speed of rotation of a cooling fan. As a result, the centrifugal force and consequent back pressure are decreased to cause opening 25' to be again opened. While the opening 25' is repeatedly opened and closed due to continuous suction, the valve element 28 is minutely vibrated to change the speed of rotation of the cooling fan with a short cycle. This is called "hunting" and deteriorates the function of the fan coupling device.